Electronic brake systems allow precisely controllable and rapid braking of a vehicle. In this context, the output signal of a brake signal transmitter, which depends on a deceleration demand of the driver, is passed to a control unit. In the control unit, the output signal of the brake signal transmitter can be additionally modified by driving safety systems, such as an antilock system, a traction control system or a system for electronic stability control. From this, the control unit produces control signals, which are passed to “brake pressure modulators”, which control the supply of a pressure medium, generally compressed air in the case of utility vehicles, to the individual braking devices or brake cylinders in a manner specific to the wheel or axle-wise by means of electromagnetically actuatable valve arrangements. In the event that said control unit fails, e.g. because the power supply thereof is interrupted, the electronic brake system generally has a redundant device associated with the service brake or the pressure control system in order to be able to bring the vehicle safely to a halt, even in this operating situation, by brake actuation.
The use of spatially and structurally separate brake pressure modulators for the individual pressure control circuits gives rise to a relatively large installation space requirement and manufacturing expense for air brake systems of the type described on light to medium-weight utility vehicles.
Given this background, DE 10 2009 009 811 A1 discloses a dual-circuit brake pressure modulator for an electronic brake system of a vehicle. The brake pressure modulator has two pressure control circuits, in which the flow paths of each circuit are fed by a dedicated pressure supply and are pneumatically separated up to the respective working pressure connection. One of the two working pressure connections is provided for connecting a brake cylinder of a left-hand wheel and a brake cylinder of a right-hand wheel of a front axle, and the other of the two working pressure connections is provided for connecting a brake cylinder of a left-hand wheel and a brake cylinder of a right-hand wheel of a rear axle. Respective pressure control valves for the operation of an antilock system are connected upstream of the brake cylinders. Each pressure control circuit is assigned a dedicated redundant control pressure circuit, by means of which a working pressure is passed to the working pressure connection of the respective pressure control circuit in the event of a failure of electric components of the brake system. Each redundant control pressure circuit is fed by a foot brake valve of a foot brake signal transmitter, which is connected pneumatically to the respective compressed air supply. A common electronic control device is provided for the two pressure control circuits of the dual-circuit brake pressure modulator, said control device producing a control signal corresponding to a setpoint working pressure for each pressure control circuit, depending on the braking demand signals from the foot brake signal transmitter. For each pressure control circuit there is a dedicated electromagnetically actuatable valve device, which produces an actual working pressure for the respective working pressure connection from the supply pressure of the associated compressed air supply in accordance with these control signals.